Magnetic transducer head structure with reduced leakage between core circuits

ABSTRACT

A magnetic core structure for a &#34;read-write&#34; transducer head of the type known as a &#34;wide-write, narrow-read&#34; head, having at least one magnetic gap, wherein the magnetic pole structure performing one of the transducing functions (e.g. the &#34;write&#34; function) is in effect wider than that performing the other (e.g. the &#34;read&#34;) function. At least one such magnetic pole has a laminar structure comprising at least one medial layer or strata and at least one flanking layer or strata which is disposed adjacent to and overlying at least portions of the medial strata, to thereby define an included area of overlap therebetween. The thickness of the medial strata, measured along the length of the gap, is less than that of the magnetic core structure on the opposing side of the gap. At least one non-magnetic isolation member is disposed between the flanking strata and the medial strata, the flanking strata, comprising a magnetic material, being disposed in magnetic communication with the medial strata, to thereby magnetically shunt portions of the medial strata. The included area of overlap between the medial strata and the flanking strata is particularly configured so as to limit the transfer of magnetic flux between the flanking strata and the medial strata across the isolation members at the included area to less than about ten percent of the total magnetic flux in the magnetic circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of co-pending application Ser. No. 915,734 filedon Oct. 6, 1986 now U.S. Pat. No. 4,819,107 which is acontinuation-in-part of Ser. No. 645,436 now abandoned.

TECHNICAL FIELD

This invention relates generally to the field of magnetic recording, andmore particularly to transducer structures used for magnetic recordingand reproducing ("read/write") operations. Still more particularly, theinvention relates to magnetic transducer core structures which areparticularly useful in digital data-storage devices, especially (but notexclusively) tape recorder devices ("tape drives") of the type used insuch applications.

BACKGROUND OF THE INVENTION

Most data storage and retrieval is done by use of magnetic recordingapparatus, mainly disc drives and tape drives (the term "drive" havingcome to be accepted as the basic industry designator forrecorder/reproducer devices). In the case of disc drives, there are both"hard" disc and "floppy" disc-type media, the "hard" disc being a rigidplatter having a magnetizable surface upon which magnetic fluxtransitions are recorded by means of a transducer head whichaerodynamically "flies" with respect to the surface of the disc, beingspaced therefrom by a thin film of air. "Floppy" disc drives utilizemagnetically recordable media which although disc-like in shape is muchmore in the nature of magnetic tape, being highly flexible and typicallycomprising a sheet of polymeric material carrying a surface coating ofmagnetizable metal oxide. In floppy disc drives, as in tape drives,recording is accomplished by maintaining direct contact between themoving media and the recording head, usually by projecting the tIp ofthe head (at the magnetic "gap") into the plane of the flexible media asit moves past the head.

Tape drives typically, or at least frequently, feature bi-directionalrecording and reproducing operation in which the tape is transportedalong its length from one end to the other during a first read or writeoperation and then transported back in the opposite direction for thenext such operation, without rewinding the tape between the twosuccessive recording operations as would usually be done in taperecording. This bi-directional operation is not characteristic in discdrives (whether "floppy" or "hard" disc media is involved), in which thedisc-form media is continuously rotated in the same direction and allrecording or reproduction on the media is done unidirectionally.

This rather fundamental difference in operational modes creates acorresponding fundamental difference in the nature of the transducers orheads which may be utilized. In the case of bi-directional reading andwriting, a multi-gap head is used, but in the case of unidirectionalrecording only a single-gap head is necessary, which is much lessexpensive than a multi-gap head but has the disadvantage of only beingable to read and write at different times; i.e., it cannot write andsimultaneously read data, as is frequently desirable and is oftenprovided for in tape drives.

Furthermore, in order to maximize the likelihood that the read gap willbe properly positioned directly over the written track on the media, twoessentially opposite approaches have come to be recognized in the artwith respect to the multi-gap heads used in tape drives. The first ofthese involves use of a write gap which is substantially wider than theread gap, such that if the read gap is nominally positioned anywherenear the center of a written track, the head is likely to be fully inregistration with the track, i.e., recorded transitions extending acrossthe entire height, i.e. length, of the gap. The second such approachinvolves use of a head having a separate erase gap disposed ahead of thewrite gap, so that the media is erased cleanly before each writingoperation takes place; thus, the writing is always accomplished on mediahaving no residual signals. In this arrangement, a read gap is usedwhich is considerably wider than the written track, so that the entirewidth of the written track is always likely to be completely straddledby the read gap. Since the separate erase gap eliminates all residual orextraneous signals recorded contiguous to the narrower written track,interference, cross-talk and the like will not be present in the readdata stream.

Since the approaches just described can only be accomplished withmulti-gap heads, they are not utilized in floppy disc drives, where onlysingle-gap read/write heads are used. In order to provide a systemsomewhat analogous to the second arrangement described above, floppydisc drives frequently utilize a "tunnel erase" concept, in whichseparate erase gaps are provided on both sides of, and to the rear of,the single read/write gap. The function of the two such erase gaps is to"trim" the marginal edges of the written data track by erasing alongboth sides thereof, thus producing a resultant narrowed track of writtendata, the sides of which have no residual or extraneous recordedtransitions. In this arrangement, the head structure is somewhat complexsince it is necessary to space the erase gaps rearwardly of theread/write gap in order to eliminate or minimize both mechanical andmagnetic interference problems, and of course there is the addedrequirement and expense of providing, and assembling, two separate erasegaps.

The tunnel-erase concept just described is not advantageous inbi-directional recording operations, since bi-directional use of thattype of head would inherently necessitate the addition of another pairof erase gaps, spaced on the opposite side of the single read/write gapfrom the location of the first such set of erase gaps, in order toaccommodate both of the possible mutually-opposite recording directions.The realities of manufacturing such a head do not favor its potentialuse, since the required accurate alignment of the various erase gapswith respect to themselves and with respect to the single read/write gapresults in a different manufacturing process which inevitably addssubstantial expense. Of course, there is also additional expenseinvolved in the requirement of the second pair of erase gaps, in and ofthemselves.

In an effort to provide a solution for the difficulties and problemsdiscussed above, it has heretofore been proposed to use a different formof core structure for such transducer heads, which in effect providesoperational characteristics functionally representative of thosetypically found in multi-gap heads, while nonetheless having in factonly a single read/write gap.

More particularly, it has been proposed in the past, to use a transducerhead whose magnetic core structure has a full-width write core disposedon one side of the gap and a partial-width read core on the oppositeside of the gap. In this structure, special additional magnetic closureor return pieces are disposed on opposite sides of the comparativelynarrow read core at the gap, to in effect fill the space created bynarrowing the read core. These additional components serve as part ofthe write core structure during write procedures but are not intended tocontribute to the read core output signal appearing on a sense coilaccessing only the read core. For examples of such transducer corestructures, reference is made to Japanese Patent Publication Nos.50-111817 (Pat. No. 5235618) and 58-171710 (Patent Abstracts Vol. 8, No.10, P. 248), as well as U.S. Pat. No. 4,085,429.

The last-mentioned of the above disclosures discusses the overridingimportance of obtaining the most favorable signal-to-noise ratiospossible in using such special-purpose transducers, and of isolating theread channel from the write channel therein, and this prior patent ispredicated upon the use of certain allegedly critical limitations forthe thickness, with respect to the magnetic gap, of isolation layersproposed for use between the narrowed read core and the specialadditional write core closures disposed on opposite sides of the readcore.

Notwithstanding the factors just noted, the prior efforts of others inthe field have until now failed to appreciate and take intoconsideration certain other highly significant factors involved in thedesign considerations for the special-purpose transducer-head corestructure involved, and the present invention is based upon, andprovides, recognition and disclosure of these important factors. Thus,the present invention provides new and valuable structural features andarrangements for such a core structure, involving improvements which areof such importance where high-density recording is involved as toultimately make the difference between successful and unsuccessfuloperation, bearing in mind the underlying requirement that in actualoperation such a device must be substantially free from spurious errorand consistently reliable in performance.

Accordingly, the present invention provides structural improvements anddesign criteria for "wide-write, narrow-read" magnetic transducer corestructures, which improvements make high-density recording operationpossible with attendant low error rates. Broadly speaking, the inventionprovides important structural and size relationships in the elementscomprising the magnetic core; more particularly, the invention providescertain critical size relationships in the area of overlap between theread core and the special write core closures which, when carriedthrough in the incorporation of isolation components (laminar elements,at times referred to as "strata"), provide the consumately desirableoperational results just noted.

The foregoing generalized features of the invention will become moreapparent following due consideration of the ensuing specification andthe appended drawings, in which a preferred embodiment is disclosed toillustrate the underlying concepts and the overall aspect of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a sectionalized overhead plan view of a transducer head corestructure in accordance with the invention, taken along the plane I--Iof FIG. 2;

FIG. 2 is an enlarged, bottom view of the structure of FIG. 1 and

FIG. 3 schematic representation showing the equivalent magnetic circuitfor the structure of FIGS. 1 and 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now in more detail to the drawings, FIGS. 1 and 2 show theoverall nature of a transducer head core structure 10 in accordanceherewith. As illustrated in these Figures, the core structure 10includes differently-structured parts (essentially halves) 12 and 14.Considering the half or portion 12 of the core structure as being the"write" portion, it will be seen that this half of the core, shown atthe left of the transducing gap 16, constitutes a single pole memberwhose height is the full height of the gap.

The portion 14 of the core structure 10, appearing at the right side ofthe transducing gap 16, is not a single monolithic structure like theportion 12, but is instead composite in form, including (in thisparticular embodiment) three different component parts disposed instratified or laminar form, designated 18, 20 and 22 respectively. Ofthese, the two outermost (side) members (sometimes referred to herein as"flanking strata") 18 and 22 comprise closures (returns) for the writecore, whereas the central or medial strata 20 comprises the read core.

As discussed more fully below, it is extremely important for each of thethree core elements, or strata, 18, 20 and 22 to be separated, i.e.magnetically isolated, from one another. For this reason, non-magneticisolation members 24 and 26 are disposed between and preferably extendat least slightly beyond the boundaries of the write closures 18 and 22,as illustrated in FIG. 2, the read core 20 extending substantiallybeyond the isolation layers.

With reference to FIG. 1, it will be seen that the core structure 10 maybe generally C-shaped in its overall configuration forming the recordinggap 16 at the opening between two converging face portions 12a and 14awhich basically define what is commonly referred to as the "cutbackangle." Bearing in mind the relative height of the different stratashown in FIG. 2, it will be seen from FIG. 1 that the main write core 12extends rearwardly from face portion 12a, has an electrical excitationor drive winding (a "write coil") 30 wound about an intermediate portionof it, and extends back toward and into contact (or other magneticcommunication) with the other half of the overall core structure at aboundary or junction 32. At this rearward location, the three coreelements 18, 20 and 22 located on the opposite side of junction 22 haveessentially the same height relationship as they do at the transducinggap 16, and thus together correspond to the full height of the writecore 12.

The upper and lower strata 18 and 22, i.e., the write closures, extendrearwardly from the transducing gap 16 in a much more direct manner thanis true of the inner or medial read core strata 20, which hasconfiguration in plan which is essentially a mirror-image to that of thewrite core portion 12 described above (FIG. 1). Also, the read coremedial strata 20 has an electromagnetic coil 28 wound about anintermediate portion 20b, which in accordance with the embodiment underdiscussion constitutes a read sense coil.

With regard to particular structural materials, the read and write cores12 and 20 and the write closures 18 and 22 may in general be of anyconventional magnetic material customarily used in transducer cores,i.e., "mu metal", ferrite, etc. The various components ("strata")constituting the different core elements may each comprise a "stack" ofthin sheet-like laminae, as is often done to reduce eddy currenteffects, but this is not really essential in transducer cores generally,particularly where (as here) the intended application is to write andread relatively narrow and closely-spaced tracks of magnetictransitions. As will be understood, the isolation layers or elements 24and 26 are to be of non-magnetic material, e.g. copper or brass, etc.Where the intended media is in the form of magnetic tape, the overallheight of the head is preferably many times greater than the mere heightof the magnetic core structure itself, and generally equals or exceedsthe total width of the tape since the latter must slide lengthwiseacross the convex (and often curved) front face of the head duringtransducing operations and the tape should be supported by the headacross its entire width. The opposite is generally true in floppy disctransducing procedures, wherein the pole pieces defining the gaptypically form a rounded, bluntly conical projection which deforms therecording media into a complementary dimple as the media moves over thegap during recording. As already indicated above, the core structure ofthe present invention may be embodied in a head of that nature also, bymerely using appropriate shape relationships and incorporating the basicstructural attributes and concepts set forth herein.

As will be understood, since the preferred embodiment in accordanceherewith refers to a transducer head for use with tape media, theoverall height of the transducer head should be much higher than themere height of a single-track core structure, such as is shown in FIG.2, the general physical structure of the head (apart from the core)being structured according to known head-building techniques, inaccordance with which a mounting block of non-magnetic material (e.g.,brass) of the desired physical size for the overall head is used tomount the magnetic core components. Usually, such a mounting block takesthe form of two complementary halves, which are joined together aroundthe outside of the core structure, interstitial spaces being filled byan appropriate non-magnetic potting compound, such as epoxy, which mayalso be used as an exterior coating or shaping agent.

A transducer head structured generally in accordance with the foregoingprovides the anomalous result of non-symmetric write/read widthcharacteristics in a single-gap core and head. In the particular formatgenerally referred to above, the write core (pole structure) 12 isconfigured, by its size and shape at the magnetic gap and thecharacteristics of the write coil winding 30, to write a track ofmagnetic transitions which are essentially as wide as the full length ofthe gap 16, i.e., the full width of core portion 12. On the other hand,the much narrower read core ("medial strata") 20 is configured, by itsown size and shape, and by the characteristics of the read coil 28 woundupon its accessible intermediate portion 20b, to read a track width muchnarrower than the write core. Consequently, the overall head structurein the arrangement noted constitutes a head of single-gap configurationwhich writes a wide track but reads a narrow one.

Somewhat more particularly, it will be seen from the above thatenergization of the write coil 30 with electrical signals which it isdesired to record will create corresponding magnetic flux patternswithin the core structure 10, travelling around the paths so defined andacross the transducing gap 16, at which position the width of the fluxat the gap is actually a function of the height or width of the writecore 12 and the overall height or width of all of the various strata(18, 20 and 22) constituting the opposite core half 14, i.e.,essentially the same width as the write wire 12. As a result, a recordedtrack of the same width is written on the media moving across the gap.

Accordingly, in a write mode, the magnetic flux which moves across thegap from core 12 to core 14 is actually returned across the rear portionof the core (i.e., across the boundary 32) by all three of the strata18, 20 and 22. In a read mode, however, the magnetic circuit performanceis different due to the relative configuration of the read core 20 andthe position of the read coil 28, which is wound upon only themedially-disposed read core element 20 and not on either of the outerstrata 18 and 22 which flank the read core; consequently, members 18 and22 function only as write closures. Thus, with the read core disposed inco-axial alignment with a written track on the media, the read core polepiece will be aligned over only the center portion of the written trackon the media, and it will thus access considerably less than the fullwidth of the magnetic transitions on the media. Accordingly, themagnetic flux flowing from the read core strata 20 to the rear boundaryor junction 32 will be substantially less than the total availablemagnetic flux within the core itself, the write closures (i.e., the"peripheral" or "flanking" strata 18 and 22) serving in effect to shuntaway from the read core a selected portion of the total magnetic fluxwhich is not desired to be represented in the output (i.e., not desiredto be "read"). Accordingly, a wide-write, narrow-read capability isprovided, even though the head has but a single magnetic gap.

As indicated above, the selectively separate performance of the readcore structure in relation to the write core structure of the disclosedapparatus is of primary importance in satisfying the desired objective.In large part, this consideration resolves itself down to the effectiveisolation of such two different core portions from one another,particularly during "read"-type transducing operation, at which time itis typical to encounter magnetic transitions on the recording media inproximity with the write closures ("flanking strata") 18 and 22 whichare not desired to be reproduced in any manner. For example, suchtransitions may simply comprise "noise" of undetermined origin, orunerased previously-recorded data, "over-write", etc. Of course, sincethe read sense winding 28 is disposed about only the read core ("medialstrata") 20, and not about the write closures 18 and 22, the effect offlux transitions encountered at the gap 16 by write closures 18 and 22will not induce a corresponding sense voltage in the read winding 28;nonetheless, it will be evident that "cross talk" may result in a numberof ways, which generally may be considered as "leakage" between thecorresponding read and write portions of the core structure, mutualinductance, etc.

In point of fact, effective isolation between the write closures 18 and22 and the read core 20, respectively, is essential in order to limitthe effects of such "noise" to the greatest extent possible. This isparticularly true where high-density digital recording is to beaccomplished and, as is well known, there appears to be a constant andcontinuing desire for ever-greater recording densities in order tomaximize data storage in relation to the physical size of the media.Whereas the isolation of these read and write core components has beenlargely overlooked by others heretofore, however, the aforementionedU.S. Pat. No. 4,085,429 provides for the use of isolating (non-magnetic)layers at the locations which have been identified; however, the entirethrust of this patent is that in order to be effective the thickness ofsuch isolation layers in relation to recording gap width is a criticalrelationship, and this prior patent states a requirement for a veryspecific range of such thickness in terms of the recording gap width.

The present invention is based upon different and alternative conceptsfrom those just noted, which have heretofore gone unrecognized.

More particularly, with reference to FIG. 3, the simplified circuitshown in this figure represents the magnetic flux present in themagnetic circuit provided by the core structure 10. In this schematic,the label "F_(total) " designates total flux flow in the magneticcircuit, and is comprised of the two branches F₂ and F₃, which representthe flux flowing through the read core and through the write closure,respectively. In this figure, the magnetic reluctance of thecorresponding core parts is represented as resistance elements, elementR₃ being the reluctance of either of the two write closures 18 or 22,R_(x) being the reluctance of either of the two isolation layers or 26,and R₂ designating the magnetic reluctance of the read closure 20 alone;thus, the effective reluctance of the read path is (R_(x) +R₂)

From the above, it will be seen that the degree of isolation in thedisclosed multi-component core structure is a function of the magneticreluctance of the write closures (R₃) in relation to that attributableto the read structure (R_(x) +R₂) Thus, ##EQU1##

Of course, ##EQU2## where ₀ is the permeability of free air,

_(r) is the permeability of the non-magnetic material used for theisolation layers,

t =the thickness of the isolation layers, and

A =the common area included between either of the write closures 18 and22 and the read closure 20, i.e., the corresponding overlap betweenthese elements.

In accordance with the above, it may be seen that it is very importantto make R_(x) large with respect to R₃. While this may be accomplishedby making the thickness of the isolation layers large in relation totheir effective area "A," this approach causes undesirable resultsbecause it produces a correspondingly wide, unrecorded "stripe" on themedia during write operations, which typically will contain variousun-erased data from previous operations. Consequently, in accordancewith the present invention the desirable result of making R_(x) largewith respect to R₃ is achieved by making the common area A (see FIG. 1)small in relation to the thickness of the isolation layers 24 and 26, inparticular of an order of magnitude sufficient to make theaforementioned flux ratio F₂ /F_(total) not more than about 5%, and inno event more than 10%. That is, the ultimate goal should be to restrictthe common area A to a value permitting no more than about 10% leakageor cross-talk , and preferably no more than about 5%, between themagnetic flux flowing in the write closures 18 and 22 and the readclosure 20 disposed therebetween. As indicated above, it is in factessential to maintain such a relationship in order to achieve reliableand consistent substantially error-free high-density digital recording.

To further and more explicitly illustrate the foregoing, the width of atypical narrowed read core 20 in accordance with the invention may be onthe order of half the total width of the write core 12 (for example fivemils and ten mils, respectively) and if the thickness (t) of theisolation members 24 and 26 is approximately one-half mil each (as is infact deemed appropriate in such a situation), the combined width of thetwo write closure members 18 and 22 will be four mils. (As will beunderstood, the two write closures will normally be of equal thickness,i.e., one-half of such combined width, although other and unequalrelative proportions may be used where this is desired.) The amount ofundesired noise resulting from flux transitions located beyond the edgeextremities of the write closures 18 and 22 and in effect "read" by thelatter during read operations is modified by these size ratios: thus,where the dimensions are as stated above, and where the maximumallowable flux leakage margin is selected to be not more than tenpercent, ##EQU3## or, stated in terms of magnetic reluctance, ##EQU4##therefore, it is desired that ##EQU5##

In a specific working example of the above, where

R₃ =6.9 10⁶

R₂ =4.4 10⁶

₀ =4 10⁷

_(r) =1

A<961 mils²

It is to be understood that the above is merely a description of apreferred embodiment of the invention and that various changes,alterations and variations may be made without departing from theunderlying concepts and broader aspects of the invention as set forth inthe appended claims, which are to be interpreted in accordance with theestablished principles of patent law, including the doctrine ofequivalents.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows.
 1. A magnetic corestructure for a transducer head particularly adapted for use in digitaldata storage devices, comprising:a magnetic circuit formed by magneticcore elements, said circuit having at least one gap defined by twoopposing sides where magnetic flux in such circuit may accessmagnetically-recordable data storage media; means forming a firstmagnetic pole structure for said circuit and defining one side of saidgap, and means forming a second magnetic pole structure for said circuitand defining the other side of said gap, generally opposite said firstpole structure; at least said first magnetic pole structure having alaminar structure comprising at least one strata and at least oneflanking strata, each comprising magnetic and having a predeterminedmagnetic reluctance; said flanking strata being disposed in adjacentoverlapping relationship with portions of said medial strata along saidgap to thereby define an included area of overlap whose magnitude isdetermined by the length and width of that portion of the flankingstrata overlying said medial strata at the gap, said medial stratahaving a thickness at said gap measured in a direction along said gapwhich is less than the thickness of said second pole structure disposedacross said gap, to thereby access a narrower recorded band on saidmedia than that accessed by said second pole structure; isolation meanscomprising at least one layer of non-magnetic material disposed betweensaid medial strata and said flanking strata at said included area ofoverlap, for magnetically separating at least said portions of saidmedial strata from the overlapping portions of the flanking strata; saidflanking strata serving to magnetically shunt portions of said magneticcircuit formed by said medial strata by extending alongside and intomagnetic communication with said medial strata at a point along saidmagnetic circuit which is spaced from said first pole structure in thedirection of said second pole structure, to thereby provide a parallelmagnetic return; said isolation means layer being thin in relation tosaid flanking strata and having a thickness less than one-half that ofthe adjacent flanking strata; and said included area of overlap betweensaid medial strata and said flanking strata at said first pole structurehaving a magnitude which makes the effective magnetic reluctance of saidisolation means layer disposed therebetween sufficiently large withrespect to the magnetic reluctance of said flanking strata that thetransfer of magnetic flux from the flanking strata to the medial strataacross the non-magnetic isolation means at said included area is limitedto less than about ten percent of the total magnetic flux present insaid magnetic circuit.
 2. A magnetic core structure as defined in claim1, wherein both of said pole structure at said gap have generally thesame overall thickness or width measured in a direction along said gap.3. A magnetic core structure as defined in claim 1, including at least apair of said flanking strata, each disposed on an opposite side of saidmedial strata and having substantially the same thickness and overlyinga selected area located between said flanking strata and said medialstrata, said selected areas both being of substantially the same size tomaintain said limited percentage of flux transfer.
 4. A magnetic corestructure as defined in claim 3, wherein both of said pole structures atsaid gap have generally the same overall thickness or width measured ina direction along said gap.
 5. A magnetic core structure as defined inclaim 1 wherein said included area of overlap between said medial strataand said flanking strata at said first pole structure has a magnitudewhich is determined in accordance with the ratio of the magneticreluctance of said flanking strata with respect to the sum of magneticreluctances of said flanking strata, said medial strata and saidisolation means layer, such that the transfer of magnetic flux from theflanking strata to the medial strata across the non-magnetic isolationmeans at said area is limited to less than about ten percent of thetotal magnetic flux in said magnetic circuit.
 6. A magnetic corestructure as defined in claim 1 wherein said included area of overlapbetween said medial strata and said flanking strata at said first polestructure has a magnitude which is less than that determined inaccordance with the expression ##EQU6## where: R₂ is the magneticreluctance of the medial strata;R₃ is the magnetic reluctance of theflanking strata; t is the thickness of the isolation means layer; and kis the permeability of free air times the permeability of the isolationmeans layer.
 7. A method of reading and writing magnetic fluxtransitions on magnetically-recordable media by using a single-gaptransducer head in a manner producing results analogous to thoseachieved by multi-gap heads, comprising the steps:transporting therecording media past a single-gap transducer head having a gap definedby two opposing sides establishing an overall gap length in a directiongenerally orthogonal to that of medial transport, and recording fluxtransitions on said media by using substantially all of the transducermagnetic core structure which defines an overall length of said gap;transporting the recording media past said transducer head in areproducing pass and, during said reproducing pass, reproducing the fluxtransitions previously recorded on said media by using a particularportion of said magnetic core structure constituting only apredetermined part of the overall length of said gap which is less thanthe overall length of said gap; disposing non-magnetic means having afirst reluctance between said particular portion of said magnetic corestructure used in reproducing flux transitions and other adjacentportions which are located along said gap length, said other adjacentportions having a second reluctance and overlapping said particularportion when viewed along said gap length, said non-magnetic meansserving to magnetically separate said particular portion of saidmagnetic core structure and said other adjacent portions during saidreproducing pass; and restricting the size of the said adjacent portionsin the area where they overlap said particular core portions in order tolimit the amount of leakage flux transfer therebetween by making thesaid first reluctance so much greater than the said second reluctancethat such leakage flux is restricted to a particular minor percentage ofthe total flux present in said core structure during reproduction ofsaid recorded transitions even though said non-magnetic means is thinnerthan said other adjacent portions as viewed along the length of saidgap.
 8. The method of reading and writing magnetic flux transitions asrecited in claim 7, wherein said step of restricting the size of saidarea of overlap comprises limiting said area to an extent which limitssaid leakage flux transfer to a value which is less than about tenpercent of the total magnetic flux flowing in said magnetic corestructure.
 9. The method for reading and writing magnetic fluxtransitions as recited in claim 8, wherein said step of restricting thesize of said area of overlap comprises making said area of overlapsufficiently small to limit said leakage flux transfer to a value notsubstantially exceeding five percent of the total magnetic flux flowingin said magnetic core structure.